ICC Color Spaces

What they are and how they work.

What they are:

A device color space simply describes the range of colors, or gamut, that a camera
can see, a printer can print, or a monitor can display. Editing color spaces, on the other hand,
such as Adobe RGB or sRGB, are device-independent. They also determine a color range you can work
in. Their design allows you to edit images in a controlled, consistent manner. A device color
space is tied to the idiosyncrasies of the device it describes. An editing space, on the other
hand, is gray balanced — colors with equal amounts of Red, Green, and Blue appear neutral. Editing
spaces also are perceptually uniform; i.e. changes to lightness, hue, or saturation are applied equally
to all the colors in the image.

What a color space contains:

Imagine a box containing all the visible colors. The farther from the center
of the box you go, the more saturated the colors become — Red towards one corner, Blue towards
another, Green towards the third (our box has a curious shape). A Cyan, Magenta, Yellow color space
works the same way, except that the primary colors are CMY rather than RGB. For simplicity, we
will refer only to RGB spaces, but the comments apply equally to CMY(K) color spaces. A color space
can be represented as a balloon blown up inside the box. The space taken up by the balloon is the
portion of the total number of visible colors that fall within the particular color space. Larger
balloons contain more colors, or have a larger gamut, while smaller balloons hold fewer colors. The
surface of the balloon has the most saturated colors that the color space can hold. Any colors falling
outside the balloon can't be reproduced in that color space.

Colors inside the balloon are described using (R,G,B) coordinates. The most saturated
(i.e. purest) red in any color space has an R-value of 255. Since larger color spaces have larger balloons,
they contain both more air volume (i.e. more colors), and the surface of the balloon is farther from
the center of the box (i.e. the colors are more saturated). Therefore, larger color spaces such as Adobe
RGB contain both more colors and more highly saturated colors than smaller spaces like sRGB. A
comparison of the Adobe RGB and sRGB gamuts is below. As you can see, working with Adobe RGB allows
you to see and print more of most colors. Adobe RGB was designed to contain the entire color gamut
available from most CMYK printers. sRGB is an HP/Microsoft defined color space that describes
the colors visible on a low end monitor.

In general, you want to use color spaces that are as large as is practical. For
example, if your printer is capable of producing output in a color space larger than sRGB, there is no
reason to hobble your work by limiting output to the small sRGB gamut. If you do, you'll lose the
saturated cyans and greens that can make your prints stand out.

What can we learn from the above?

Your applications and devices need to know what color space they are working with.

This most definitely
includes your monitor. Without knowing what color space
your monitor displays images in, it is impossible to accurately gauge how your images will appear in
print. Calibration and profiling of your monitor is the first step towards a color managed workflow.

Most printers and very
few scanners or cameras either print or capture images in well-defined color spaces.

Larger color spaces contain both more colors and brighter, more saturated colors.

If
your camera or scanner supports it, use a larger color space such as Adobe RGB.

Use sRGB for web graphics.
This is at least in the same ballpark as most monitors. Using
Adobe RGB for web images leads to washed-out looking colors in applications that are not color aware
(i.e. most web browsers).

Viewing Color Spaces

You can compare standard color spaces to those of many common printers, digital cameras, and scanners using our interactive color gamut plots. These are 3-D models that allow you to view the color spaces from all angles.